The roof might have caved in on Tottenham's European adventure with a 4-0 mauling at the Bernabéu, yet the Champions League would not be the competition it is if the going did not get tough at the quarter-final stage and there was no real shock value in tournament debutants suffering at the hands of Real Madrid. The much bigger surprise was in the other quarter-final, where the holders took the lead after 25 seconds then shipped an astonishing five goals against Schalke.

It is a moot point whether Spurs' task in having to overcome a 4-0 deficit in the home leg is better or worse than Internazionale having to travel to Germany and score four goals to no reply to progress – with a 5-2 lead from the away leg any other scoring pattern would see the away goals rule working strongly in Schalke's favour – though the likelihood is that neither mountain will be climbed and Spurs and Inter will go out. If so, another year will go by without a side managing to hang on to the Champions League trophy. Real Madrid, Benfica, Inter, Ajax, Bayern Munich, Milan, Liverpool and Nottingham Forest all claimed back-to-back wins of the old European Cup – when there were no more than half a dozen ties and the winners were invited back every year. Conditions then seemed to lend themselves to repeat performances. Yet since the present Champions League format arrived in 1993 no side has successfully defended the trophy.

Perhaps Inter were never going to be a good bet to break the pattern once their extra ingredient had decamped to Real Madrid, though no one was expecting last year's winners to blow up quite so spectacularly on home ground. Most teams in European competitions have never recorded a win at the San Siro, or can count the number of times they have on the fingers of a mitten. Winning 5-2 is ridiculous, and while Sir Alex Ferguson and Carlo Ancelotti would have opted to play the Bundesliga runners-up in preference to the Italian holders before the first leg kicked off, there is always something dangerous about German teams on a roll of confidence, especially when they can boast seasoned campaigners such as Edu and Raul within their ranks.

While Inter are not the same team as last season without José Mourinho at the helm, a trip to the San Siro for a Champions League semi-final remains daunting. The Veltins-Arena in Gelsenkirchen sounds much less intimidating, unless you are one of the England players who lost to Portugal there in the 2006 World Cup, though under Ralf Rangnick Schalke appear to be putting a run together similar to the one Borussia Dortmund achieved under Ottmar Hitzfeld in 1997. No one gave the unfancied Germans much of a chance then, either. But they put out Manchester United and went on to beat Juventus in the final. Juventus were holders and overwhelming favourites to win again, especially given the upstart nature of their opponents in the final, yet here was an early example of the Champions League's capacity to come up with a fresh surprise every year.

The only surprise this year will be if Barcelona do not win it. They are clear favourites based on the way they are playing, not simply because of their reputation or pedigree. The only thing that stopped them last season was Inter's superb defensive organisation under Mourinho. The same manager now seems likely to lie across Barcelona's path in the semi-final, though nothing Real Madrid have achieved in La Liga this season, particularly head-to-head against Barcelona, suggests that Mourinho's new team can defend with as much discipline and determination as his old one.

Like Barcelona, Manchester United appear a shoo-in for their domestic league, Arsenal and Chelsea challenges having fallen away of late, yet there the similarity ends. This has been one of Barcelona's most convincing seasons and one of United's least. By common consent they lead the Premier League almost by default so it was surprising to hear Ferguson blowing the trumpet for a possible second treble. There is no doubt they can do it – when you have the league virtually sewn up, have reached the FA Cup semi-final and can see a path to the Champions League final you might as well accentuate the positive – and as Ferguson says, if anyone can rise to the challenge of 14 games over a two-month period United can. They are used to that sort of challenge, and even when below their eye-catching best they can doggedly stagger on like few others.

What is surprising about Ferguson's new bullishness was that only a couple of weeks ago he was saying that one major trophy would constitute a successful season. That seemed a sensible line to take, setting the bar at a certain height and accepting anything else as a bonus. "To win one trophy would be great but we have to take the chance of winning all three now, we can repeat the treble," he said this week. It would appear that Ferguson has added to the motivation of Chelsea in the Champions League and Manchester City in the FA Cup semi-final, as well as increasing the pressure on his own players. He probably knows what he is doing, but the logic of loading one of his less celebrated sides with the extra weight of expectation is hard to follow. Two years ago, faced with an FA Cup semi against Everton and an eventual Champions League meeting with Barcelona in Rome, Ferguson sacrificed one and lost the other.

Now he is boldly talking of trying for another treble with a side that does not look quite as good to most people, Javier Hernández's emergence and Wayne Rooney's fitful contributions notwithstanding. Perhaps Ferguson simply wants to emphasise what United are all about and put glory back at the heart of the enterprise, instead of all the sordid side issues that have been detaining all concerned with the club over the past couple of weeks. Fair play, if that is the case, though no club has a monopoly on glory. Plenty of other teams also can't get enough of it, from City to Chelsea, Schalke to Barcelona. One cannot help but feel that this version of Manchester United might have to share a bit of it around.